The system called tower weight was the more general name for King Offa's pound. This dates to 757 AD and was based on the silver penny. This in turn was struck over Arabic dirhams (2d). The pound was based on the weight of 120 Arabic silver dirhams, which have been found in Offa's Dyke. The same coin weight was used throughout the Hanseatic League. The tower system was referenced to a standard prototype found in the Tower of London and ran concurrently with the avoirdupois and troy systems, until it fell out of use and was abolished in 1527.